[Courtesy of Dave Wenzlick [slickraft "at" uswest.net], August 1999]
I have used two basic techniques to cover large or small EPP planes. The most common method of covering EPP consists of misting the parts with Super 77 spray glue and then covering with Ultracoat /Oracover. This method is used to perfection by such notable EPP builders as Dave Sanders and Wade Kloos.
I started using the other method of using packing tape and sign vinyl here in Arizona, because the Super 77 would release at the high temperatures we see here in Phoenix. (It can easily reach 160 F inside my truck and between the Super 77 getting soft and the EPP swelling in the heat, the Ultracoat would literally fall off.) Using the method detailed below, the builder will have more options available in obtaining a scale finish. It will be slightly heavier than the Super 77/Ultracoat method and you need to decide for yourself, based on where you fly and the type of finish you desire, if the packing tape/sign vinyl system is the best choice for you. I'll let Super 77/Ultracoat users explain their tricks.
Here is an explanation of how Steve Willcox and I have covered our EPP ships. Some examples are my 1/7 scale P-40 and micro BD-5J's and Steve's Glasair III and Polen Special that were all recently in the Model Airplane News article by Dave Garwood. The basic airframe should be built and sanded as usual for either method. I try to carve the EPP with sharp knives or razors as much as possible to rough in the contours.
From there I almost exclusively use drywall sanding screen to form the EPP the final shape. Vacuum off the dust and EPP tidbits. Next using a solvent based contact cement such as Weldwood brand (used to attach laminates to countertops) coat the EPP parts with a thin layer of contact cement. I use a small sponge and a glove. You can also use a small stiff brush or even a scrap of EPP to squeegee a thin layer onto the parts. It doesn't take much so spread it thin.
When the glue is getting old and thickened I have thinned it with lacquer thinner to allow it to spread out easier. The contact cement will allow the strapping or packing tape to stick aggressively to the foam and the bond won't release when it gets hot. You can do one side of the wing and let it dry for a while and then coat the other side. I also like the contact cement because when it is dry it is only mildly tacky.
Super 77 will cause you to pickup every little bit of dust and dirt while you are trying to cover your part. The contact cement should be completely dry before you cover it. If your plane needs strapping tape for strength then put it on now before you begin covering with the packing tape. My P-40 has some strapping tape and my little BD-5J's don't need any. Do not pull the packing tape any tighter than needed to lay it down without wrinkles. You can warp the airframe if you try to get it too tight. I use packing tape to begin covering the airframe. If you like the colored packing tape then you can use it and save adding color later. In this case you would not need any sign vinyl except for decals or lettering. On my P-40 I needed colors and details that colored packing tape just wouldn't provide. You can't paint over packing tape and get decent adhesion of the paint.
So the next step is to cover the airframe with clear packing tape such as 3M Highlander tape. On the wings I start at the sub trailing edge and lay a strip from tip to the center. Don't over stretch the tape. Just lay it down smooth. I then lay on the next piece overlapping the first by at least a 1/4 ". When you shrink the tape later you don't want to pull apart a seam. Continue laying on the tape forward to the leading edge.
Now flip the wing over and starting at the sub trailing edge again, repeat the taping forward. On the tips I leave it about an inch long and roll it around to the opposite surface. I usually add one more pieces of tape on the leading edge for dent protection. Try not to get the tape more than 2 layers thick in any large areas. It makes it harder to heat and shrink a thicker area without accidentally burning through the adjoining tape.
I now tape the other wing half the same way. For the fuselage I usually start at the rear and work forward. Don't try to cover compound curves with one large piece of tape. It is better to use several small pieces. The seams on the tape edges are easier to hide than a wrinkle. On nose and canopy curves go slow and use smaller pieces. Also, try to roll the tape around into any cut outs for servos, access hatches, canopies etc. If you don't the edges will sometimes pull up when you shrink it.
For small slits, such as stab slots or rudder slots, just cover over them and cut the slots back open later. Now that everything is covered in packing tape it should be ready to shrink. I use a heat gun but an iron will work especially in small areas where the heat gun would be too intense. On the wing shrink the edges first and make sure they are sealed down, then work on the center. Just like with iron on coverings be sure you are not inducing a twist or warp as you shrink. After the shrinking is done, rub down the surface to be sure it is stuck down good. Pop any bubbles you might see. If you burn through an area or pop a seam, trim the damage and apply a packing tape patch and shrink again.
Now it's time to apply the vinyl. The vinyl provides you a flexible, colorful, paint-able (if needed) surface. The vinyl provides little strength on its' own. The packing and strapping tape are used for strength. I purchase premium grade sign vinyl from instant sign shops around town. Try to get the 1.5-1.7 mil thickness. It stretches and sticks down better. I normally buy white because I am going to paint over it. If you see a color you like, save some painting and buy the colored vinyl. Metallic colors and some of the reflective colors are way too thick so avoid these.
Wipe down the area you are going to cover to make sure it is clean. On large flat areas such as a wing panel you can sometimes lay down a large piece of vinyl if you float it on with a mixture of 1 gallon of water and a few drops of soap sprayed on the surface first.
On war birds, where there will be panel lines anyway, I lay down the vinyl dry, in smaller pieces. The edges of the vinyl will always show a little, just like any seam would, but from about 5 feet away you can't see them. You certainly won't see them as it speeds by you in the air. Again, I prefer to work from back to front when applying the vinyl. The vinyl will stretch nicely around curves but be careful not to stretch it too much as it tends to creep back a little.
On my P-40 I covered the entire airframe in white because I was painting it in camouflage colors on top and light blue underneath. I like to let the vinyl set for a day or two in a warm area if possible to let any wrinkles appear or see if any vinyl might creep a little because I pulled it too tight.
Work on the radio gear and get the rest of the plane built. I tend to paint the vinyl as late as possible in the building process so everything else is ready to go. I used a 1/4" balsa sheet tail group on the P-40 and I just applied the sign vinyl straight down on the clean sanded wood. I installed the tail group and linkages before I painted the P-40.
When it's ready to paint I dampen a cloth lightly with mineral spirits to clean the vinyl and slightly soften the vinyl surface. Don't saturate the vinyl or let it soak under the seams. Now mask as required with a good, but not too aggressive tape. Vinyl electrical tape is good.
I have used Testors, Krylon, Rustoleum and even some water based airbrush paints. I strongly recommend testing on some scraps first. When in doubt I paint several scraps of vinyl and when completely dry I lay down some masking tape on it and try to see how well the paint has stuck by yanking off the tape.
After painting let it all cure well and add any graphics, panel lines, decals etc. you wish. I sometimes will apply a clear matte finish (test again for compatibility) to seal down the decals and details.
That's the basics of my covering technique.
If you want to check out the result see the web sites listed. I have been very pleased with the results. I got carried away on the P-40 and airbrushed on landing gear, oil leaks, exhaust smoke etc.
P-40 Warhawk http://www.users.uswest.net/~slickraft/p40page.htm
Slickraft BD-5J http://www.users.uswest.net/~slickraft/BDflier.htm